A method for transfecting nucleic acid to cell comprising a step for forming a nucleic acid complex by bringing a double-stranded nucleic acid molecule into contact with a nucleic acid carrier having an amino acid sequence of alternating a basic amino acid and a hydrophobic amino acid, which has a peptide chain that forms a β-sheet structure in which a side chain of a positively charged basic amino acid is disposed on one surface side and a side chain of a hydrophobic amino acid is disposed on the opposite surface side in the presence of the double-stranded nucleic acid molecule having a double helix structure, and by binding the double-stranded nucleic acid molecule and the peptide chain through either one or both of the electrostatic interaction between the side chains of the basic amino acid and phosphate groups and hydrogen bonds between the double stranded-nucleic acid molecule and the peptide chain and a nucleic acid complex used for the same are disclosed.